1. Field of the Invention
The present invention relates generally to subsea well installations, more specifically, to a tool used for connecting a flowline apparatus to a subsea well installation.
2. Background of the Prior Art
Different structures are placed on or buried in the seabed for subsea oil and gas production operations. The base structures have mandrels or tubular members to connect to flowlines. Flowlines connect these structures and are typically installed after the structures were placed at the seabed. The lines or piping systems with connectors at the ends are lowered to the seabed for installation via wire rope guidelines or other running strings such as pipe. The connectors are consequently hard landed on either the subsea mandrel or support structures, and with the aide of tools and remote operated vehicles (ROV), are locked to the tubular members. The tubular members are typically vertical so the flowline connectors lower down on top of them, but the mandrels can be horizontal. If the connector assemblies are landed fast or too hard on the tubular members such that the landing force is not controlled, damage to the hubs and seals can occur.
Flowline connector assemblies are normally run subsea and landed over the tubular members with funnel up, funnel down, or frame and tool assemblies. Prior art assemblies required the ROV to perform numerous operations in order to engage locking members from the remotely run frame to the subsea base structure. Earlier assemblies also required the ROV to perform numerous operations to engage locking members on the flowline connector, even after the frame has been secured to the subsea support structure.
Later assemblies have a frame holding the connector spaced above the tubular member when the frame lands on the structure. The frame hard lands on the structure to bear most of the landing forces and aligns the connector with the tubular member. The frame then lowers the connector until it abuts the tubular member or soft lands on the tubular member. In these assemblies, the frames were either mounted to the connector or the frames were removeable. The removeable frames used dogs to engage the connector.
When dogs were used, hydraulic pressure held the dogs in substantial contact with the connector. In the event of hydraulic pressure failure, a mechanical back-up was necessary. Many times the hydraulic systems would fail. The back-up systems had to be actuated with ROVs, which cost the operator time and money. Furthermore, whenever a hydraulic system failed, the entire frame would have to be lifted to the surface for repairs, which also accounted for losses of production time and money.
The tool in this invention uses at least one ring assembly to hold the connector that it is attaching to the mandrel or tubular member. The each ring assembly includes at least one dog that is moved between radially inward and outward positions. The dog is positioned within a cam ring that partially surrounds the connector. When the dog is moved radially inward, the dog is in its gripping position to hold a connector. Each dog has a cam pin or follower running therethrough. The follower also extends through a cam slot on the cam ring. When the follower moves relative to the cam ring, it can only move along the cam slot. The dog cannot move relative to the follower, so the dog moves in unison with the follower along the path allowed by the cam slot.
The cam slot has a radial inner portion and a radial outer portion, so the follower and the dog move radially inward and radially outward along the cam slot. The ring assembly also includes a cam follower ring that engagingly slides relative to the cam ring. A portion of the follower engages the cam follower ring. The follower can only move radially with respect to cam follower ring, therefore relative circumferential movement between the cam ring and the cam follower ring is in unison between the cam follower ring, the follower, and each dog. The cam ring can be moved relative to the cam follower ring, which forces the follower to move radially inward or outward as cam slot moves around the follower. Therefore the dogs can be opened or closed by moving the cam ring.
Each dog includes at least one protrusion or protuberance on its outer circumference. When each dog is radially outward, the protuberance fits into a recess formed in the cam ring so that both the protuberance and the outer circumference of each dog is in substantial contact with the cam ring. As each dog moves radially inward the dog also moves circumferentially relative to the cam ring. The combination of the radial and circumferential movement of the dog relative to the cam ring moves the dog so that the protuberance is positioned where the outer circumference of the dog had been positioned rather than against a recess. A gap is formed between the outer circumference of the dog and the cam ring because the protuberance extends beyond the outer circumference of the dog to the cam ring. The protuberance remains in substantial contact with the cam ring. Thus, any radially forces from the inner circumference of the dog are absorbed by the cam ring. No hydraulic pressure is needed to keep the dogs in their closed position, and there is no need for a mechanical back-up because the cam ring is a physical barrier to outward movement of each of the dogs.